JP2005079571A - Sectional zero-phase-sequence current transformer - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a winding method for reducing residual current in a sectional-track-type ZCT for use in a cabinet panel for low-voltage circuit. <P>SOLUTION: Four coils having the same number of active turns and the same conductor diameter of a coil material are connected in parallel to each together, thereby a residual current is reduced in a sectional-track-type ZCT. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a split type zero phase current transformer used in a low voltage distribution board or the like.

  The split type zero-phase current transformer can be installed in the distribution board without stopping electricity. Therefore, when a ground fault is detected with the transformer class B grounding wire, it is possible to detect the fault point early by exploring the fault feeder in the distribution board using a split-type zero-phase current transformer. .

  The wiring in cubicles and distribution boards may be arranged in a row. As such an application, there is a divided track type ZCT. The split-type zero-phase current transformer has poor residual current characteristics due to the rectangular shape of the window and the split location in the magnetic path. Therefore, in order to improve the characteristics, the magnetic shield used around the iron core is generally provided more than the non-divided one. As a result, the finished dimensions are large, heavy, and expensive.

As a method for solving these problems, there is a system in which the secondary coil is made independent for each coil approaching the primary current to form three coils and they are connected in parallel. A leakage current is generated in the iron core by the primary current. This leakage flux is linked to the secondary coil, and a circulating current flows between the secondary windings by the induced voltage. The magnetic flux generated by this current reduces the leakage flux of the primary current and reduces the residual current. (Patent Documents 1 and 2).
Japanese Patent Publication No. 6-58857 Announcement of Japanese Patent Publication No. 8-33424

  The problem to be solved is that the residual current is still large even in the split track type ZCT using three coils. The reason why the residual current is generated in the split track type ZCT using three coils will be described.

  FIG. 1 shows a system using the above three conventional coils. The primary conductors A, B, and C are arranged in a line. IA, IB, and IC are primary currents. A secondary winding is wound around the iron core 1. The coil 2 has a lot of interlinkage with the leakage magnetic flux caused by the primary current IA. Similarly, the coils 3a and 3b are largely linked to the leakage magnetic flux caused by the primary current IB. The coil 4 also has a lot of linkage with the leakage magnetic flux caused by the primary current IC. The sum of the number of turns of the coil 2 and the number of turns of the coils 3a and 3b and the number of turns of the coil 4 are the same, and the wire conductor diameter is also the same.

The primary current is a low-voltage three-phase balanced current as shown in FIG. At this time, consider the magnetic flux interlinking with the coil 2 as an example. The magnetic flux interlinking with the coil 2 includes φA from the primary current IA, φB from the primary current IB, and φC from the IC. The sum of these interlinkage magnetic fluxes can be expressed as one interlinkage magnetic flux φa. The magnetic flux interlinking with the coils 3a and 3b can also be expressed as φb as the sum of the magnetic flux from each primary current, and the magnetic flux interlinking with the coil 4 can also be expressed as φc. Since each coil can be expressed as an interlinkage magnetic flux with one magnetic flux, each coil can be expressed as an influence of a magnetic flux from a one-phase current. That is, it can be considered as a combination of CT having three gaps as shown in FIG. If the primary currents at this time are Ia, Ib, and Ic, the relationship between the currents IA, IB, and IC shown in FIG. 1 (2) and these Ia, Ib, and Ic can be expressed in FIG. 2 (2). The current Ia affecting the coil 2 can be expressed by the vector sum of the influence from the primary current IA (IA), the influence from the IB (IBA), and the influence from the IC (ICA). Similarly, Ib and Ic can be expressed as vector sums of the components (IB), (ICB), (IAB), (IC), (IAC), and (IBC) of the respective primary currents. When zero phase current is not included, IA + IB + IC = 0. Similarly, Ia + Ib + Ic = 0. FIG. 2A is represented by an equivalent circuit as shown in FIG. N2 is the number of turns of each coil, I0 is a zero-phase current, Ze is an excitation impedance, and Irs is a residual current flowing on the secondary side. r is the resistance value of the coil, and rb is the resistance value of 3a + 3b. For three parallel windings, rb = r. When the residual current Irs is obtained from the equivalent circuit of FIG. 3, equation (1) is obtained.

ここで

である。Ｚ_ｅ≫Ｚ_２、Ｚ_ｅ≫ｍ_２、よりＩ_ｒｓの１次換算残留電流Ｉｒは次式となる。

Here, assuming that the current flowing on the secondary side when the zero-phase current I ₀ flows is I _O2 , I ₀₂ is obtained from the following equation.

here

It is. From Z _e >> Z ₂ , Z _e >> m ₂ , the primary equivalent residual current Ir of I _rs is given by the following equation.

  Here, the sum obtained by multiplying the magnetic field strength in each coil by the magnetic path length is 0 and the residual current is also 0 based on the law of circulatory integration of amperes. However, in order to change to the output voltage, the magnetic permeability is related as a coefficient, and the magnetic permeability changes depending on the magnitude of the magnetic field of the soft magnetic material (usually using a permalloy PC material of iron-nickel alloy). In the arrangement as shown in FIG. 1, the magnitudes of the equivalent primary currents Ia and Ib are different between the coil 2 and the coil 3a. When the interlinkage magnetic flux with the coil 2 by the equivalent primary current Ia is 0.2 to 0.3 T (Tesla) less than the magnetic saturation, the interlinkage magnetic flux with the coil 3a is compared to φa: φb≈5: 1. At this time, if the permeability of φa is μa and the permeability of φb is μb, this ratio is μa: μb≈2: 1. Therefore, in equation (4), the magnetic permeability in each coil is different, so ma ≠ mb and a residual current is generated.

  In the present invention, in order to solve the above-mentioned problem, the coils 3a and 3b wound around the IB are independent from each other, and two coils wound around the IA and IB are added to the coils 3a and 3b. Were connected in parallel.

これにより（４）式の〔〕内は０に近づくことができる。In the present invention, the residual current can be reduced by using four coils as compared with the case of using three coils. With the four coils, rb shown in the equation (4) becomes rb = r / 2. As for mb, mb≈ (1/2) ma is obtained from the difference in the magnitude of magnetic permeability compared to ma, μa: μb≈2: 1, and the following equation is obtained.

As a result, the value in [] in equation (4) can approach zero.

  FIG. 6 shows the effect of the invention. In FIG. 6, the horizontal axis represents the number of coils connected in parallel, and the vertical axis represents the residual current. The number of parallel connections of the coil is 1 in FIG. 5 (1), the number of connections is 2 in FIG. 5 (2), the number of connections is 3 in FIG. 3, the number of connections is 4 in FIG. Show. When the number of connections is 4, the residual current is minimized. As a result, if the usage fee of the iron core and the shielding material is the same as the conventional one, the residual current is halved. If the residual current characteristics are the same, the cross-sectional area of the conventional core or shield can be reduced to about ½. That is, the size and weight can be reduced, and the amount of iron core (usually a soft magnetic material of nickel alloy) can be reduced, saving resources. Low cost can be realized.

  In the primary conductors IA, IB, and IC arranged in the divided track type ZCT window, the coil wound on the two sides in the major axis direction close to IB is wound as uniformly as possible, and the intermediate point of one coil is closest to the primary conductor IB. Determine the position of the coil so that The four coils have the same number of turns.

  FIG. 4 shows the structure of the divided track type ZCT of the present invention. The coils 3a and 3b wound in the vicinity of the primary conductor IB have the same number of turns and the same conductor diameter as that of the coil 2, the number of turns and the wire. Therefore, the number of turns and the wire of all four coils were the same, and the outputs were connected in parallel. FIG. 4 shows a rectangular shape with respect to the primary conductors IA, IB, and IC. However, even in the case of an elliptical shape, the coil is wound in the same way and connected with the same effect.

FIG. 1 (1) shows an example of the connection of the secondary winding of the track type zero-phase current transformer, and shows the case where the coil has three parallel connections. (2) represents a primary current vector. FIG. 2 (1) shows the track type zero-phase current transformer shown in FIG. 1 (1) as CT having three gaps. (2) represents the primary current as a vector when the magnetic flux interlinking with the coils of the three CTs is expressed as an influence of each one current. 3 is a simplified equivalent circuit diagram of FIG. FIG. 4 shows an example of connection according to the present invention in which a coil approaching the primary current IB is divided into two coils to form four parallel connections. FIG. 5 shows connection examples of the secondary winding of the track type ZCT. (1) is a continuous winding of a coil, (2) is a 2-parallel connection, and (3) is a 5-parallel connection with three coils near IB. FIG. 6 shows the residual current value converted to the equivalent primary-side zero-phase current value when the number of parallel connections of the coils is changed in a state where the primary current is constant at 600A of the three-phase current.

Explanation of symbols

A, B, C: primary conductors IA, IB, IC for primary current arranged in a line in a window of the track type ZCT 1-phase primary balanced current 1 ... of the track type ZCT Coil 3a wound around the part where the iron core approaches A in the iron core 2 ... 3 parallel winding 3a coil 3b wound around one side of the two parts where the iron core approaches B in the 3 parallel winding -Coil 4 wound around the other side of 3a among the two parts where the iron core approaches B in the three parallel windings ... Coil φA wound around the part where the iron core approaches C in the three parallel windings ... Magnetic flux φB interlinked with coil 2 generated from primary current IA ... Magnetic flux φC interlinked with coil 2 generated from primary current IB ... Coil 2 and chain generated from primary current IC Magnetic flux r ... DC resistance value Ia of one coil ... Coil 2 Current Ib when the intersecting magnetic flux is a magnetic flux generated by a single current, current Ic when the magnetic flux interlinking with the coils 3a and 3b is a magnetic flux generated by a single current, ... Coil 4 When the magnetic flux linked to the coil is a magnetic flux generated by one current, the current φa is the sum of the magnetic fluxes φA, φB, and φC, and the magnetic flux φb that is linked to the coil 2 by the current Ia. Magnetic flux φc interlinked with 3a, 3b... Magnetic flux interlinked with coil 4 by current Ic... Mutual inductance mb of coil 2 with respect to current Ia ... of coil 2 with respect to current Ib Mutual inductance mc ... Mutual inductance (IA) of coil 2 with respect to current Ic ... Component of current IA (IBA) applied to magnetic flux of coil 2 ... Applied to magnetic flux of coil 2 Component of current IB (ICA): component of current IC applied to magnetic flux of coil 2 (IB): component of current IB applied to magnetic flux of coil 2 (IAB): current IA applied to magnetic flux of coil 2 Component (ICB): current IC component applied to magnetic flux of coil 2 (IC) component of current IC applied to magnetic flux of coil 2 (IAC) component of current IA applied to magnetic flux of coil 2 (IBC): The component N2 of the current IB applied to the magnetic flux of the coil 2 ... the number of turns of one coil I0 ... the zero phase current Ze ... the exciting impedance Irs of the zero phase current transformer ... the residual current

Claims (2)

  Divided track type characterized in that in the secondary winding wound around the iron core, four coils having the same number of turns and the same winding material diameter are connected in parallel to reduce the residual current. Zero-phase current transformer.   It has a secondary winding wound around the iron core and a tertiary winding wound with a magnetic shield material covering the periphery of the secondary winding. Both the secondary and tertiary windings are composed of four coils. A split track type zero-phase current transformer characterized in that both are connected in parallel to reduce residual current.

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